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An estimate of soil mineralizable N is needed to determine crop needs for N fertilizer. The objective of this research was to estimate soil net N mineralization in soils maintained in continuous corn ( Zea mays L.) (CC), corn–soybean Glycine max (L.) Merr. (CS), and corn–soybean–wheat ( Triticum aestivum L.)/alfalfa ( Medicago sativa L.)–alfalfa (CSWA) rotations that have been managed since 1990 with zero N (0N), low N (LN), and high N (HN) fertilization. Soil samples were taken from 0‐ to 20‐cm depth in plots planted to corn in 1998. In order to produce more realistic time‐series data of net N mineralization, soils were incubated in filtration units in a variable‐temperature incubator (VTI) that mimicked field soil temperatures under a growing corn canopy. Rotation and N fertilization significantly affected net N mineralization in soil samples. Cumulative net N mineralized in a 189‐d field temperature incubation averaged 133 ± 6 kg ha −1 in CC, 142 ± 5 kg ha −1 in CS, and 189 ± 5 kg ha −1 in CSWA. Across rotations, average net N mineralized was 166 ± 9 kg ha −1 in 0N plots, 147 ± 10 kg ha −1 in LN plots, and 152 ± 10 kg ha −1 in HN plots. Inclusion of a legume, particularly alfalfa, in the rotation increased net N mineralized. Generally, more net N was mineralized from plots receiving no fertilizer N than from soil with a history of N fertilization. Variable‐temperature incubation produced realistic time‐series data with low sample variability.
Carpenter‐Boggs et al. (Wed,) studied this question.